The present invention relates to a method of manufacturing glued laminated wood made of a number of wood sheets such as veneer sheets which are provided by rotary peeling or otherwise prepared, dried appropriately, clipped into a predetermined length, and laminated together by hot pressing with a thermosetting adhesive in such a way that a continuous length of multiple-layered board of glued laminated wood is made. Wood sheets in each layer of the resulting glued laminated wood board are disposed in a staggered relation to wood sheets in the adjacent layer in the lengthwise direction of the board. The invention also relates to an apparatus for manufacturing such glued laminated wood.
For better understanding of the underlying background of the present invention, firstly reference is made to FIG. 1 which schematically shows a prior art apparatus for manufacturing laminated veneer lumber (LVL), that is a typical glued laminated wood, wherein a number of veneer sheets are laminated together in a staggered manner with the wood grain of each veneer sheet running primarily along the length of the resulting product or LVL board.
The apparatus includes three sets of hot presses X, Y and Z arranged at three different stages spaced at an interval along the direction in which LVL board in process is conveyed as indicated by arrow at the right-hand side on the drawing. Each of the hot presses X, Y and Z has a pair of movable upper and lower heating plates X1, Y1 and Z1 disposed one above the other, respectively. For the sake of description of the apparatus, these three sets of hot presses X, Y and Z will be referred to as the first, second and third hot presses, respectively. Though not shown specifically in the drawing, there are provided three sets of veneer feeders associated with the respective hot presses X, Y and Z, and each set includes upper and lower movable veneer sheet feeders as indicated by arrows which depict the feeding directions. In the drawing, reference symbols A, B and C designate wood veneer sheets each having substantially the same length, width and thickness and disposed in the same orientation with the wood grain thereof extending substantially parallel to each other, i.e. extending along the lengthwise direction of the LVL board in process. It is noted that, for the sake of convenience in illustration, each veneer sheet is illustrated with a thickness which is shown exaggeratedly large relative to its length and also that a conveyer for moving a board in process is omitted from the illustration.
In manufacturing LVL board with the apparatus of FIG. 1, firstly a pair of veneer sheets A depicted by shading is prepared with one surface of either one of such veneer sheets A coated with thermosetting adhesive. These veneer sheets A are fed by the first feeders for the first hot press X and combined together with the adhesive-coated surface interposed between the mating surfaces of the two veneer sheets A and with the ends thereof in an offset or staggered relation as shown in the drawing in such orientation that their wood grain extends generally along the length of LVL board to be produced. These two veneer sheets A thus placed one on the other are conveyed to the first pressing station between the first heating plates X1, where the veneer sheets A are glued together under heat and pressure by the hot press X. After the first hot pressing operation is over and the heating plates X1 are retracted, the laminated veneer sheets A are conveyed toward the second pressing station at the second hot press Y.
On the way to the second pressing station, i.e. at an appropriate position between the first and second pressing stations, another pair of veneer sheets B, indicated by shading, each having on one surface thereof adjacent to the laminated veneer sheets A coated with thermosetting adhesive is fed by the second veneer sheet feeders and laid on the opposite outer surfaces of the previously laminated veneer sheets A in a staggered relation to the veneer sheets A as shown in the drawing. The veneer sheets B thus laid onto the veneer sheets A are conveyed therewith to the second pressing station, where the veneer sheets B are pressed by the second hot press Y to be bonded to the laminated veneer sheets A.
After pressing by the second hot press Y is over, the laminated veneer sheets A and B are conveyed toward third hot press Z at the third station. At an appropriate position between the second and third pressing stations, still another pair of veneer sheets C, indicated by shading, having on the inner surfaces thereof coated with adhesive is fed by the third veneer feeders and laid on the opposite outer surfaces of the veneer sheets B in a staggered arrangement. The veneer sheets C thus placed on the laminated veneer sheets A and B are conveyed to the third pressing station, where they are similarly pressed by the third hot press Z. Thus, an assembly of laminated veneer sheets A, B and C is formed.
Steps of operation including the above veneer sheet feeding, laying, hot pressing and conveying are performed successively at the respective positions and stations, whereby an LVL board with six plies as counted through its thickness is formed. As shown in FIG. 1, any two adjacent veneer sheets A, B or C in each layer are disposed with the ends thereof abutting closely each other to form end joints, and the veneer sheets A, B and C are laid such that the end joints are distributed in a regularly staggered arrangement in the resulting LVL board.
For successful gluing of veneer sheets with the desired bonding strength, heat and pressure should be applied as uniformly as possible to the entire surface of each veneer sheet to be bonded. In bonding a pair of veneer sheets A, B or C by hot pressing according to the method as illustrated in FIG. 1, however, part of the surfaces of the paired veneer sheets fails to receive direct pressing action by the heating plates of the hot press. That is, the areas of veneer sheets A, B and C adjacent to their upstream end portions as viewed in the conveying direction, which are indicated by R, fail to be pressed directly by the heating plates of the hot press, although some heat will be conducted to such area of veneer sheets. As a result, the upstream end portions of veneer sheets will not be bonded with the desired strength, thus affecting the quality of the resulting LVL product.
If veneer sheets are laid in such a staggered array that the area R is narrowed or reduced with an attempt to obviate the above drawback, the end joints in any two adjacent layers of the LVL board will be disposed closer to each other, thereby rendering the board weaker against bending.
Therefore, it is an object of the present invention to provide a method and apparatus of manufacturing glued laminated wood such as LVL which can solve the above-described problem.